Generally, steam pipes are used as part of a district heating system in many cities carrying steam from central power stations under the streets to heat, cool, or supply power to high rise buildings and businesses. Some businesses and facilities also use the delivered steam for cleaning and sterilization. In addition to providing space and water heating, the steam is used in numerous restaurants for food preparation, laundries and dry cleaners, as well as to power absorption chiller systems for air conditioning. One of the concerns to such a system is the excitation of water hammer that may lead to serious consequences including damaged vents, traps, regulators and piping. The water hammer is caused by accumulation of condensed water that is trapped in a portion of horizontal steam pipes. The velocity of the steam flowing over the condensed water causes ripples in the water creating buildup of turbulence resulting in the water formation of a solid mass or slug that fills the pipe. The slug of the condensed water can travel at the speed of the steam striking the first elbow that is encountered in its path. The force can be comparable to a hammer blow and can be sufficiently large to break the back surface of the elbow.
The above referenced U.S. Pat. Nos. 8,632,244 B2, 9,404,891 B2, and 9,586,234 B2, the disclosures of which are incorporated herein by reference in their entireties, describe systems and methods that can provide real-time monitoring of fluid level (e.g., height) in pipes that operate at high temperature and elevated pressure. Results of such monitoring can be provided to data handling systems for further action based on the results, and/or provided for display and monitoring purposes. According to such referenced patents, measurement of fluid height at a location inside the pipes is provided by a single piezoelectric transducer that launches an ultrasonic probe signal into the pipe, without mechanically penetrating the wall of the pipes. Reflected ultrasonic signals are captured by a transducer, which can be the same transducer that launched the probe signal. The reflected signals are subjected to data processing, which can include filtering, amplification, analog-to-digital conversion and autocorrelation analysis. A result is extracted which is indicative of a property of the fluid, such as a height of a condensed fluid, a cavitation of the condensed fluid, and a surface perturbation of the condensed fluid.
Similar ultrasonic range measurement techniques are well known in the art, and have been used in wide range of applications, including sonar, robotic ranging, and medical imaging. In principal, a single piezoelectric transducer is used for sending and receiving an ultrasound wave (signal) via piezoelectric effects, and a thickness value of a target bulk (e.g. fluid medium) is obtained by measuring a trip time of the ultrasonic wave multiplied by a corresponding wave velocity in the medium divided by two (taking into account the ultrasonic wave path, back and forth, through the target bulk).
The above measurement methods based on a single transducer generally work when the surface of the fluid is normal, or substantially normal, to the propagating wave front of the ultrasound wave (e.g., steady-state condition), otherwise, as in the case of a fluid under turbulent flow conditions, the ultrasonic wave is refracted or scattered and is not returned for detection at the single (piezoelectric) transducer.
Therefore, there is a need for systems and methods that can provide improved and accurate measurement of fluid contents of piping systems not only under steady-state conditions, but also under turbulent flow conditions.